Adaptive suppression of subordinate reproduction in cooperative mammals

在许多合作繁殖的动物中，每组中的一只占主导地位的雌性实际上垄断了生殖，其他雌性帮助抚养后代。然而，在大多数动物社会中，从属雌性有时会繁殖，在少数物种中，大多数成熟雌性经常繁殖。理解这些差异的原因，以及控制雌性生殖分布和生殖倾斜程度的行为和生理机制，对于解释合作的进化、个体的生殖策略和合作繁殖者的种群动态至关重要。然而，尽管20多年来生殖偏斜的变异一直是行为生态学研究的重点，但还不可能解释从属繁殖在物种之间或物种内的分布。以前解释下级繁殖频率的尝试要么假设下级雌性在优势雌性给予她们生殖优惠以确保它们留在群体中并帮助抚养后代的地方繁殖，要么假设下级繁殖在支配地位无法阻止它们怀孕或哺育幼崽的地方繁殖。另一种可能性是，压制或驱逐从属雌性会对支配者的健康造成巨大代价(部分原因是从属雌性通常是她们的女儿或姐妹，部分原因是支配者的繁育成功取决于居民帮手的数量)，以及从属繁殖频率的差异是压制从属于支配者的净收益不同的结果。虽然一些相关的证据表明情况可能是这样，但还没有研究衡量从属繁殖对占主导地位的雌性的成本，也没有研究确定压制从属的净收益的变化是否会影响从属繁殖的频率或被支配的雌性赶出群体的频率。到目前为止，研究控制生殖偏差的最终和最接近机制的最好方法是控制从属和优势种的繁殖频率，并确定这如何影响优势种的繁殖成功及其对从属种的处理。根据现有的喀拉哈里猫鼬Suricta suricatta的研究种群，在这个种群中，所有的个体都是可识别的，并且可以获得多个种群在15年内在生长和繁殖成功方面的个体差异的详细记录，我们将使用定量比较和实验相结合的方法来操纵从属和优势种的繁殖频率，(1)衡量从属繁殖对支配者的成本(2)确定压制从属于支配者的净收益的差异是否影响它们容忍从属的程度(3)确定支配者是否监控从属的成长并有选择地将可能的挑战者从群体中驱逐出去(4)确定支配者是否试图影响其可能继任者的身份(5)建立广义博弈论模型，该模型可用于预测支配者容忍从属的程度、生殖倾斜的程度以及其他社会脊椎动物群体的大小和结构。

In many animals that breed cooperatively, one dominant female in each group effectively monopolises reproduction and other females help to rear her offspring. However, in most animal societies, subordinate females sometimes breed and, in a few species, most mature females breed regularly. Understanding the reasons for these contrasts and the behavioural and physiological mechanisms controlling the distribution of reproduction among females and the degree of reproductive skew is of central importance in explaining the evolution of cooperation, the reproductive strategies of individuals and the population dynamics of cooperative breeders. However, although variation in reproductive skew has been the focus of considerable research in behavioural ecology for more than twenty years, it has not yet been possible to account for the distribution of subordinate breeding either between or within species. Previous attempts to explain the frequency of breeding by subordinates have either assumed that subordinate females breed where dominant females grant them reproductive concessions to ensure that they remain in the group and assist in rearing their offspring or that subordinates breed where dominants are incapable of preventing them from conceiving or rearing young. An alternative possibility, which has received relatively little attention, is that suppressing or evicting subordinate females has substantial costs to the fitness of dominants (partly because subordinate females are commonly their daughters or sisters and partly because the breeding success of dominants depends on the number of resident helpers) and that differences in the frequency of subordinate breeding are a consequence of variation in the net benefits of suppressing subordinates to dominants. While some correlational evidence suggests that this may be the case, no studies have yet measured the costs of subordinate breeding to dominant females or have determined whether variation in the net benefits of suppressing subordinates affects the frequency with which subordinates breed or are evicted from the group by dominants. By far the best way to investigate the ultimate and proximate mechanisms controlling reproductive skew is to manipulate the frequency of breeding by subordinates and dominants and to determine how this affects the breeding success of dominants and their treatment of subordinates. Drawing on an existing study population of Kalahari meerkats Suricta suricatta, where all individuals are recognisable and detailed records of individual differences in growth and breeding success are available for multiple groups over fifteen years, we shall use a combination of quantitative comparisons and experiments manipulating the frequency of reproduction by subordinates and dominants, to (1) measure the costs of subordinate breeding to dominants (2) determine whether variation in the net benefits of suppressing subordinates to dominants affects the extent to which they tolerate subordinates (3) determine whether dominants monitor the growth of subordinates and selectively evict likely challengers from the group (4) determine whether dominants attempt to influence the identity of their likely successors (5) develop generalised game-theory models that can be used to predict the extent to which dominants tolerate subordinates, the degree of reproductive skew and the size and structure of groups in other social vertebrates.